Detailed explanation of sample code for interface definition in Java

This article mainly introduces the detailed explanation of the definition and example code of interface in Java. Friends in need can refer to the following

Detailed explanation of the definition of interface in Java

1. Define the interface

Use interface to define an interface. Interface definitions are similar to similar definitions, and are also divided into interface declarations and interface bodies. The interface body is composed of constant definitions and method definitionsgrouped. The basic format for defining an interface is as follows:

[修饰符] interface 接口名 [extends 父接口名列表]{
[public] [static] [final] 常量;
[public] [abstract] 方法;
}

Modifier: Optional, used to specify the access rights of the interface, the optional value is public. If omitted the default access permissions are used.

Interface name: Required parameter, used to specify the name of the interface. The interface name must be a legal Java identifier. Generally, capital letters are required.

extends Parent interface name list: optional parameter, used to specify which parent interface the interface to be defined inherits from. When using the extends keyword, the parent interface name is a required parameter.

Method: The methods in the interface are only defined but not implemented.

For example, define an interface for calculation, in which a constant PI and two methods are defined. The specific code is as follows:

public interface CalInterface 
{ 
 final float PI=3.14159f;//定义用于表示圆周率的常量PI 
 float getArea(float r);//定义一个用于计算面积的方法getArea() 
 float getCircumference(float r);//定义一个用于计算周长的方法getCircumference() 
}

Note:

Like Java class files, the file name of the interface file must be the same as the interface name.

Implementing the interface

After the interface is defined, it can be implemented in the class. To implement an interface in a class, you can use the keyword implements. Its basic format is as follows:
[modifier] class [extends parent class name] [implements interface list]{
}

Modifier: Optional parameter, used to specify the access permission of the class. The optional values ​​are public, abstract and final.

Class name: Required parameter, used to specify the name of the class. The class name must be a legal Java identifier. Generally, capital letters are required.

extends Parent class name: Optional parameter, used to specify which parent class the class to be defined inherits from. When using the extends keyword, the parent class name is a required parameter.

implements Interface list: optional parameter, used to specify which interfaces this class implements. When using the implements keyword, the interface list is a required parameter. When there are multiple interface names in the interface list, separate them with commas.

When implementing an interface in a class, the method name, return value type, number and type of parameters must be completely consistent with those in the interface, and all methods in the interface must be implemented. For example, write a class named Cire, which implements the interface Calculate defined in Section 5.7.1. The specific code is as follows:

public class Cire implements CalInterface 
{ 
 public float getArea(float r) 
 { 
  float area=PI*r*r;//计算圆面积并赋值给变量area 
  return area;//返回计算后的圆面积 
 } 
 public float getCircumference(float r) 
 { 
  float circumference=2*PI*r;  //计算圆周长并赋值给变量circumference 
  return circumference;   //返回计算后的圆周长 
 } 
 public static void main(String[] args) 
 { 
  Cire c = new Cire(); 
  float f = c.getArea(2.0f); 
  System.out.println(Float.toString(f)); 
 } 
}

In class inheritance, only single inheritance can be done, and the interface can be implemented When , multiple interfaces can be implemented at one time, and each interface is separated by a comma ",". At this time, constant or method name conflicts may occur. When solving this problem, if the constants conflict, you need to explicitly specify the interface of the constant. This can be achieved through "interface name.constant". If a method conflict occurs, you only need to implement one method. The following is a detailed introduction to the solution to the above problem through a specific example.

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